Method and apparatus for downhole spectroscopy

ABSTRACT

Apparatus and method for estimating a property of a downhole fluid including a carrier that is conveyed in a borehole, and a semiconductor electromagnetic energy source carried by the carrier, the semiconductor electromagnetic energy source having an active region that includes one or more nitride-based barrier layers that are modulation-doped using a nitride-based doped layer.

BACKGROUND

1. Technical Field

The present disclosure generally relates to well bore tools and inparticular to apparatus and methods for downhole formation testing.

2. Background Information

Oil and gas wells have been drilled at depths ranging from a fewthousand feet to as more than 5 miles. Wireline and drilling tools oftenincorporate various sensors, instruments and control devices in order tocarry out any number of downhole operations. These operations mayinclude formation testing, fluid analysis, and tool monitoring andcontrol.

The environment in these wells present many challenges to maintain thetools used at depth due to vibration, harsh chemicals and temperature.Temperature in downhole tool applications presents a unique problem tothese tools. High downhole temperatures may reach as high as 200° C.(390° F.) or more, and sensitive electronic equipment usually requirescooling in order to work in the hazardous environment. An added problemis that space in the carrier assembly is usually limited to a few inchesin diameter.

SUMMARY

The following presents a general summary of several aspects of thedisclosure in order to provide a basic understanding of at least someaspects of the disclosure. This summary is not an extensive overview ofthe disclosure. It is not intended to identify key or critical elementsof the disclosure or to delineate the scope of the claims. The followingsummary merely presents some concepts of the disclosure in a generalform as a prelude to the more detailed description that follows.

Disclosed is an apparatus for estimating a property of a downhole fluidincluding a carrier that is conveyed in a borehole, and a semiconductorelectromagnetic energy source carried by the carrier, the semiconductorelectromagnetic energy source having an active region that includes oneor more nitride-based barrier layers that are modulation-doped using anitride-based doped layer.

A method for estimating a property of a downhole fluid includesconveying a carrier in a borehole and carrying a semiconductorelectromagnetic energy source in a borehole using the carrier, thesemiconductor electromagnetic energy source having an active region thatincludes one or more nitride-based barrier layers that aremodulation-doped using a nitride-based doped layer. The method mayfurther include emitting electromagnetic energy from the emitter towardthe downhole fluid in-situ and detecting an interaction between theemitted electromagnetic energy and the downhole fluid using a detector.The downhole fluid property is estimated at least in part using anoutput signal from the detector.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed understanding of the present disclosure, reference shouldbe made to the following detailed description of the severalnon-limiting embodiments, taken in conjunction with the accompanyingdrawings, in which like elements have been given like numerals andwherein:

FIG. 1 is an exemplary wireline system according to several embodimentsof the disclosure;

FIG. 2 is a cross section view of a non-limiting semiconductorelectromagnetic energy source;

FIG. 3 illustrates a band diagram of the electromagnetic energy sourceof FIG. 2;

FIGS. 4 and 5 illustrate a non-limiting example of a p-downphotodetector according to the disclosure; and

FIG. 6 is a non-limiting example of a downhole spectrometer that may beused with systems such as depicted in FIG. 1;

FIGS. 7 and 8 illustrate downhole Raman spectrometer examples accordingto several embodiments of the disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure uses terms, the meaning of which terms will aidin providing an understanding of the discussion herein. As used herein,high temperature refers to a range of temperatures typically experiencedin oil production well boreholes. For the purposes of the presentdisclosure, high temperature and downhole temperature include a range oftemperatures from about 100° C. to about 200° C. (about 212° F. to about390° F.).

FIG. 1 schematically illustrates a non-limiting example of a wirelineapparatus 100 according to several disclosed embodiments. In the exampleshown, a well borehole 110 traverses several subterranean formations102. The well borehole 110 will typically be filled or at leastpartially filled with a fluid mixture which can include various gases,water, drilling fluid, and formation fluids that are indigenous to thesubterranean formations penetrated by the well borehole. Such fluidmixtures are referred herein to as “well borehole fluids”.

A formation evaluation tool 120 is conveyed in the well borehole 110using a wire line 104. Wire line deployment and retrieval may beperformed by a powered winch carried by a service truck 108, forexample. The wireline 104 typically is an armored cable that carriesdata and power conductors for providing power to the formationevaluation tool 120 and to provide two-way data communication between atool processor 112 and a controller 114 that may be carried by theservice truck 108. The wireline 104 typically is carried from a spool116 over a pulley 118 supported by a derrick 122. The spool 116 may becarried by the truck 108 as shown for on-land operations, by an offshorerig for underwater operations, or by any other suitable mobile or fixedsupporting structure. The controller 114 may include a processor 142,such as within a computer or a microprocessor, data storage devices,such as solid state memory and magnetic tapes, peripherals, such as datainput devices and display devices, and other circuitry for controllingand processing data received from the tool 120. The surface controller114 may further include one or more computer programs embedded in acomputer-readable medium accessible to the processor 142 in thecontroller 114 for executing instructions contained in the computerprograms to perform the various methods and functions associated withthe processing of the data from the tool 120.

The exemplary wireline FIG. 1 operates as a carrier for the formationevaluation tool 120, but any carrier is considered within the scope ofthe disclosure. The term “carrier” as used herein means any device,device component, combination of devices, media and/or member that maybe used to convey, house, support or otherwise facilitate the use ofanother device, device component, combination of devices, media and/ormember. Exemplary non-limiting carriers include drill strings of thecoiled tube type, of the jointed pipe type and any combination orportion thereof. Other carrier examples include casing pipes, wirelines,wireline sondes, slickline sondes, downhole subs, bottom hole assemblies(BHA's), drill string inserts, modules, internal housings and substrateportions thereof.

The lower portion of the formation evaluation tool 120 may include anassembly of several tool segments that are joined end-to-end by threadedsleeves or mutual compression unions 124. An assembly of tool segmentssuitable for the present invention may include a hydraulic, electrical,or electro-mechanical power unit 126 and a formation fluid extractor128. The formation fluid extractor 128 may include an extensible suctionprobe 138 that is opposed by bore wall feet 140. Both, the suction probe138 and the opposing feet 140 may be hydraulically orelectro-mechanically extensible to firmly engage the well borehole wall.Construction and operational details of a suitable fluid extraction tool128 are thoroughly described by U.S. Pat. No. 5,303,775, thespecification of which is incorporated herein by reference.

A large displacement volume motor/pump unit 130 may be provided belowthe extractor 128 for line purging. A similar motor/pump unit 132 havinga smaller displacement volume may be included in the tool in a suitablelocation, such as below the large volume pump, for quantitativelymonitoring fluid received by the tool 120. One or more sample tankmagazine sections (two are shown 134, 136) may be included for retainingfluid samples from the small volume pump 132. Each magazine section 134,136 may have several fluid sample tanks 106.

In several embodiments to be described in further detail later, the tool120 includes a downhole spectrometer or other evaluation tool using oneor more semiconductor components for generating and/or detectingelectromagnetic energy.

FIG. 2 is a cross section view of a non-limiting gallium-nitridesemiconductor 200 for use in hazardous environments including a downholeenvironment. The gallium-nitride semiconductor 200 may be constructedfor operation as any number of semiconductor device, for example adiode, a transistor, a field effect transistor (FET), a laser diode orany other useful semiconductor device using a high-gain media. Theexample gallium-nitride semiconductor 200 in FIG. 2 illustrates asemiconductor electromagnetic energy source that may be carried into awell borehole for use in downhole spectroscopy. Any carrier may be usedto carry the electromagnetic energy source into a well borehole. Forexample, a carrier comprising a wireline as described above and shown inFIG. 1 may be used. In several embodiments, suitable carriers mayinclude drill strings of the coiled tube type, of the jointed pipe typeand any combination or portion thereof, casing pipes, wirelines,wireline sondes, slickline sondes, downhole subs, bottom hole assemblies(BHA's), drill string inserts, modules, internal housings and substrateportions thereof.

The electromagnetic energy source 200 may be configured to emitelectromagnetic energy having a wavelength responsive to downhole fluidcharacteristics. In one or more embodiments, the electromagnetic energysource 200 may comprise a substrate 202, and an electromagnetic energyemitter 204 that includes an electromagnetic energy generating section206.

In one or more embodiments, the substrate 202 may include several layersforming a template. In one or more embodiments, the substrate 202 may bea hetero-epitaxial lateral overgrowth or more simply, hetero-ELOtemplate 202. The example shown in FIG. 2 illustrates a hetero-ELOtemplate that includes a template substrate 208 with a buffer layer 210disposed on the template substrate 208. An underlying layer 212 isdisposed on the buffer layer 210 and an interlayer 214 is disposed onthe underlying layer 212. A nitride-based layer 216 is then disposed onthe interlayer 214.

The template substrate 208 may be selected from any suitable materialfor forming a semi-conductor substrate. In one embodiment, a sapphirematerial may be used for the substrate 208. In another example, siliconcarbide (SiC) or other ceramic may be used. The buffer layer 210 may bea low-temperature buffer layer (LT-Buffer Layer) formed using one ormore nitride-based materials such as gallium nitride, aluminum nitride,and gallium aluminum nitride. The underlying layer may utilize anitride-based material. In one example, the underlying layer includesgallium nitride. The interlayer 214 may be a low-temperature aluminumnitride interlayer (LT-AlN interlayer). The top nitride layer may beselected in part based on the preceding layer materials used. In thisexample, an aluminum-gallium-nitride (AlGaN) layer is used as the topnitride layer.

The electromagnetic energy emitter 204 may be configured to emitelectromagnetic energy of any suitable wavelength or band ofwavelengths. In one or more embodiments, the electromagnetic energyemitter emits a broad band of electromagnetic energy. In one or moreembodiments, the electromagnetic energy source 200 includes afluorescent material disposed on a surface of the electromagnetic energyemitter that provides an output approximating a white light source. Inone or more embodiments, the electromagnetic energy source 200 comprisesa structure for emitting ultra-violet (UV) light. In one or moreembodiments, the electromagnetic energy source 200 may include astructure for emitting light having a wavelength corresponding to violetlight, e.g. about 405 nm. In one or more embodiments, the wavelength maybe in a range of about 380 nm to about 450 nm. In one or moreembodiments, the electromagnetic energy emitter 204 may operate as a UVlaser diode, a violet light laser diode or there may be a combination ofUV and violet laser diodes. In one or more embodiments, a laser diodemay be grown on a hetero-epitaxial lateral overgrowth or more simply,hetero-ELO template.

The UV or violet laser diode 204 in this example includes anelectromagnetic energy generator 206, which in this example is amultiple quantum well structure. Those skilled in the art with thebenefit of the present disclosure will appreciate that structures otherthan MQW may incorporate the concepts described herein. Thus, otherelectromagnetic energy generators 206 are within the scope of thedisclosure. Examples include, but are not limited to, single quantumwells, quantum dots, quantum dash structures, and quantum wirestructures.

The electromagnetic energy emitter 204 includes a lower cladding layer218 and a guide layer 220 is disposed on the lower cladding layer 218.In one non-limiting example, the lower cladding layer 218 is ann-cladding layer formed using AlGaN and the guiding layer 220 is formedusing GaN. The MQW 206, is formed using alternating barrier layers 222of InGaN material and p-AlGaN blocking layers 224. The number of barrierlayers 222 and blocking layers 224 may be selected depending on thenumber of quantum wells desired. In this example, three quantum wellsare formed using two AlGaN blocking layers 224 for raising the energyband of the wells as shown in the band diagram of FIG. 3. An interlayerlayer 226 formed using InGaN operates as a guide layer and one or morep-cladding layers 228 are disposed on top of the MQW section 206. Thep-cladding layers may be strained layer superlattice cladding layersformed using AlGaN and/or GaN.

FIG. 3 illustrates a band diagram of the electromagnetic energy sourceof FIG. 2. The AlGaN electron blocking layers increase the well depthshown in FIG. 3 at 308. The increased well depth provides betterperformance at high ambient temperatures such as those to be expected ina downhole environment. FIG. 3 is an illustrative conduction banddiagram that may be produced where a semiconductor device is constructedin accordance with the device 200 shown in FIG. 2. The Ec band 300includes a portion 302 associated with the n-AlGaN cladding layer 218. Asecond band portion 304 is associated with the GaN guide layer 220. Thenon-limiting structure of FIG. 2 forms 3 MQWs 306 with the extendeddepth 308 being associated with the p-AlGaN electron blocking layers224. The Ec band diagram then has a portion 310 associated with theInGaN guiding interlayer 226. In one or more embodiments, the Ec levelfor sections 304 and 310 are substantially the same where the materialratios are the same. A section 312 is associated with the p-AlGaN or GaNsuperlattice cladding layers 228 and includes one or more additionalblocking layers.

The exemplary semiconductor device 200 described above also illustratesa method of modulation doping that includes modulating the doping of thebarrier layers used in quantum wells. Modulating the doping according tothe disclosure may be used to shift the Fermi levels and provides a highbarrier that helps in the high temperature environment. Modulationdoping also increases absorption due to a high concentration of carrierscaused by the doping. This tradeoff is useful in the downholeenvironment and is counterintuitive with respect to the currentdirection of surface applications for laser diodes. The doping alsodecreases the electrical resistance of the device. One may also increasethe band offset by changing the alloy composition ratio to increase ordecrease the strain. Using a highly doped MQW in a GaN device alsoallows for the creation of intra-cavity contacts that facilitates themanufacturing process.

It should be understood that those skilled in the art with the benefitof the present disclosure will appreciate that other high-gainsemiconductor devices may be constructed using the nitride-basedsemiconductor and/or active region blocking layers described herein. Inseveral non-limiting examples, the semiconductor device may be a diode,a transistor, a field effect transistor (FET), a laser diode or anyother useful semiconductor device using a high-gain media. In severalembodiments, the high-temperature high-gain media semiconductor device200 may be modified for use in any number of sensor, communication,switching, amplification and information handling applications.

FIGS. 4 and 5 illustrate a non-limiting example of a p-down photodiodeaccording to the disclosure. FIG. 4 is a cross section of a photodiode,also referred to as a photodetector 400. The photodetector 400 may beused to detect any number of electromagnetic energy responses. Inseveral embodiments, the photodetector 400 may be incorporated in adownhole tool, such as the tool 120 described above and shown in FIG. 1.In one or more embodiments, the photodetector 400 may be used inconjunction with the electromagnetic energy source 200 described aboveand shown in FIG. 2.

The non-limiting photodetector 400 is a semiconductor photodetector thatincludes a substrate 402 and a multi-layer structure disposed on thesubstrate. The substrate 402 may include any suitable substratematerial. In this example, the substrate includes SiC to provide asubstrate for a high temperature photodiode, which may also be used asan avalanche photodetector. Avalanche photodetectors are used slightlyabove their breakdown voltage and are specifically designed to multiplythe electrons rather then the holes. This is due to a higher noisecaused by hole multiplication. SiC has a high ratio of themultiplication coefficients for electrons/holes and therefore will be abetter suited material system for making avalanche devices.

An n-type layer 404 is disposed on the substrate. A multiplying layer406 is disposed on the n-type layer 404. A blocking 408 layer isdisposed on the multiplying layer 406 and an absorption layer 410 isdisposed on the blocking layer 408. A cap layer 412 is positioned on theabsorption layer 410 and a mask 414 is deposited over the device withaccess openings for an upper electrode 416 and a lower electrode 418.The electrodes 416, 418 may be arranged in a p-up or p-downconfiguration. The configuration shown here is a p-up configurationwhere the p-electrode is position on an upper mesa of the device.

In operation, electromagnetic energy, which may be in the form of lightwaves 420, engages the photodiode from above the substrate as shown. Thelight interacts with the device and an output signal indicative of thelight intensity may be detected by connecting one or more leads to theelectrodes 416, 418.

The performance of the photodetector may be improved for operation in adownhole environment or other harsh environment by use of the p-carrierblocking layer 408 as shown in this example. The structure size, such asthe diameter of the detector wafer may be increased to reduce seriesresistance and to provide better thermal properties. Increasing thediameter of the wafer also provides for an easier optical couplingscheme.

Those skilled in the art will appreciate that a high-temperaturesemiconductor device, such as the device 200 described above and shownin FIG. 2 may be used in any number of applications. In one or moreembodiments, the high-temperature semiconductor device 200 may be usedas part of a downhole spectrometer. Several spectrometer examples willbe provided below with reference to FIGS. 6-8.

FIG. 6 schematically illustrates a non-limiting example of a downholespectrometer 600 according to the disclosure. The downhole spectrometer600 may be incorporated into any of several wireline tools, includingthe formation evaluation tool 120 described above and shown in FIG. 1.In other embodiments, the downhole spectrometer may be incorporated intoa while-drilling tool, such as the tool 120.

The downhole spectrometer 600 in the example shown includes anelectromagnetic energy source 602. In one or more embodiments, theelectromagnetic energy source 602 may include a nitride-basedsemiconductor as described above and shown in FIG. 2 at 200. In one ormore embodiments, the electromagnetic energy source 602 may include anarray of individual sources 622. The electromagnetic energy source 602emits energy in the form of light toward a formation fluid cell 604 viaan optical path 620. The optical path may be any path that providesoptical transmission. In one embodiment, the optical path 620 mayinclude an air gap. In another embodiment, the optical path 620 includesan optical fiber. In one or more embodiments, the optical path 620 maybe a direct interface where the electromagnetic energy source 602 isadjacent the window 606 or is in contact with the fluid 608.

The fluid cell 604 includes at least one window 606 for receiving theemitted light, so that the light may interact with fluid 608 within thecell 604. Several configurations of sample cells and windows may be usedin other embodiments without departing from the scope of the presentdisclosure. For example, to measure optical transmittance through acell, one could use a pair of windows. Transflectance measurements maybe conducted using a single window with a mirror behind the window andhaving the fluid sample between the mirror and window. Attenuatedreflectance measurements may be conducted using a single window incontact with the fluid sample. Raman scattering and fluorescencemeasurements may be conducted using a single window and collecting theresulting light on the same side of the window as the source light. Inanother example, light may be collected through a second window forRaman scattering and fluorescence measurements. Depending on the opacityof the sample, the second window could collect the resulting light at 90degrees from the direction of the source light.

Continuing with the example of FIG. 6, a photodetector 610 receives thelight after the light interacts with the fluid 606. The photodetector610, which may be a single broadband photodetector, is responsive tolight emitted from the array and provides an output signal indicative ofthe light received at the photodetector 610 after interaction with thefluid 608. In one or more embodiments, the photodetector 610 may be aSiC photodetector or a GaN detector substantially similar to thephotodetector 400 described above and shown in FIG. 4. In some cases,the photodetector output signal may be an analog electrical signal. Ananalog-to-digital converter 612 may be used to convert the photodetectoroutput signal into a digital signal that is received by a processor 624that is part of a controller 614, 616. The light emitted from theelectromagnetic energy source 602 may be modulated by the processor 624within the same controller 614 that receives the photodetector output orby a separate controller. In the example shown, one modulator/controller614 is coupled to the photodetector 610 and a secondmodulator/controller 616 is coupled to the electromagnetic energy source602. These controllers may be implemented as a single controller withoutdeparting from the scope of the disclosure. In other embodiments, thecontroller or controllers 614, 616 may be located at the surface of thewell borehole. The light emitted from the electromagnetic energy source602 may be controlled (i.e. modulated) by the controller processor 614,616. The processor 614, 616 that receives the detector 610 output signalmay also receive a signal from the controller 614, 616 modulating theelectromagnetic energy source 602.

In one embodiment, the electromagnetic energy source 602 may include oneor more light-emitting semiconductors used as individual light sources622. For example, the electromagnetic energy source 602 may includenitride-based laser diodes as described above and shown in FIG. 2. Thelaser diodes may all be coupled to a single optical fiber 620, and lightfrom that fiber would interact with the fluid 608 (through transmissionor through attenuated reflection) and afterwards be detected by thephotodetector 610. In other embodiments, the downhole spectrometer 600may include arrayed electromagnetic energy sources 602 that are not alllasers, i.e. optical channels that have a wider bandpass (lessresolution) than a laser. In these embodiments, an array oflight-emitting diodes (LED) may be used.

Cooling one or more of these downhole components may be accomplishedusing a cooling device 618. The cooling device 618 used may be anynumber of devices, examples of which include thermal-electric,thermo-tunneling, sorption cooling, evaporators, and Dewar. Cooling isoptional where components selected are compatible with the downholetemperature environment. Cooling may be applied where a componentoperating temperature is lower than the downhole environment and/or werecooling may enhance performance of the component. In severalembodiments, the electromagnetic energy source 602 is compatible withthe downhole temperature environment. Cooling in some cases couldimprove photodetector signal-to-noise ratio and increase laserbrightness. In one or more embodiments, the photodetector 610 comprisesa nitride-based construction compatible with the downhole environment.In one or more embodiments, the photodetector 610 comprises a SiCconstruction, a material with a wider bandgap compared with GaN andtherefore with a better high temperature performance.

Turning now to FIG. 7, a schematic diagram illustrates a Ramanspectrometer 700 that may be used downhole for analyzing fluid withdrawnfrom a formation. Oil-based mud contamination in a formation fluid maybe determined using Raman spectroscopy. UV Raman spectroscopy is onepart of the spectrum that is of interest due to the large gap betweenthe fluorescence emission and Raman emission. Wide band gapsemiconductor materials such as GaN and SiC are excellent candidates foroptical sources and detectors in the UV range. These materials possesssuperior thermal characteristics due to their wide band gap. For examplephotodetectors built in accordance with the present disclosure and usingSiC materials have low leakage current at high temperature. Furthermore,laser diodes described herein, reduced thermal rolloff. In one or moreembodiments, a downhole spectrometer may use a reflectance Ramanmeasurement set-up. The Raman signal in the 250 nm case, for example, isonly about 5 nm away from the pump and a Raman filter may be used toprevent the pump signal from reaching the photodetector. Such filtersare commercially available. In one or more embodiments, a SiCphotodetector or a GaN device can be used.

The Raman spectrometer 700 in FIG. 7 includes a nitride-basedelectromagnetic energy source 710. In one or more embodiments, theelectromagnetic energy source 710 may include one or more nitride-basedUV lasers used to induce or pump UV light 712 into a fluid 720 through awindow 714 made into a wall of a fluid chamber 716. The light path fromthe electromagnetic energy source 710 to the window 714 may be anoptical fiber such as the fiber 620 described above and shown in FIG. 6.The electromagnetic energy source 710 of this example includes multiplelasers producing UV light within a relatively narrow wavelength band.Alternatively, the UV electromagnetic energy source 710 may producemultiple monochromatic (single wavelength) UV light from each of severallasers. The light 722 interacts with the fluid 720 and a portion of thelight is reflected back to a detector 730.

The detector 730 according to one or more embodiments may be a SiCphotodetector or a nitride-based photodetector such as a GaN detector.The detector 730 produces a signal responsive to the light, which signalis received by a controller 750 for analysis. The controller 750 mayfurther be used as a modulator for the electromagnetic energy source 710to modulate the light emitted from the source 710.

An advantage of a UV laser diode such as one made from GaN is that,because of its wide bandgap, the laser can operate better at hightemperature in that there is less dimming and less chance of lasingcessation than when using a narrower bandgap laser at the hightemperatures encountered downhole. Here, the wide bandgap may beextended for better temperature performance using modulation doping asdescribed above with reference to FIG. 2.

Raman spectroscopy is based on the Raman Effect, which is the inelasticscattering of photons by molecules. In Raman scattering, the energies ofthe incident or pumped photons and the scattered photons are different.The energy of Raman scattered radiation can be less than the energy ofincident radiation and have wavelengths longer than the incident photons(Stokes Lines) or the energy of the scattered radiation can be greaterthan the energies of the incident photons (anti-Stokes Lines) and havewavelengths shorter than the incident photons. Raman spectroscopyanalyzes these Stokes and anti-Stokes lines. The spectral separationbetween the optical pump wavelength and the Raman scattered wavelengthsform a spectral signature of the compound being analyzed. Oil-based mudfiltrate often has a distinct spectral signature due to the presence ofolefins and esters, which do not naturally occur in crude oils. In thisway, Raman spectroscopy can be used to calculate the percentage of oilbased mud filtrate contamination of crude oil samples as they are beingcollected downhole. One can continue withdrawing and discarding oilremoved from the downhole formation until the contamination falls belowa desired level, and then the clean sample may be diverted into a samplecollection tank. However, fluorescence from aromatics in the fluidsample, often has much higher intensity, and can interfere or obscurecertain Raman signals. By using source lights having a wavelength around250 nm or less, the Raman spectrum is completed at wavelengths shorterthan those at which fluorescence begins and, therefore, interference iseliminated.

Thus, in one aspect, the electromagnetic energy source 710 produces UVlight at wavelengths near or below (shorter than) 250 nm. The detector730 may be a SiC or GaN detector as described above that can detectspectra of the Raman scatters corresponding to the light emitted by thesource 710.

The light detected by the detector 730 passes to the controller 750. Thecontroller may include a processor 752, and memory 754 for storing dataand computer programs 756. The controller 750 receives and processes thesignals received from the detector 730. In one aspect, the controller750 may analyze or estimate the detected light and transmit a spectrumof the Raman scattered light to a surface controller using a transmitter758. In one aspect, the controller 750 may analyze or estimate one ormore properties or characteristics of the fluid downhole and transmitthe results of the estimation to a surface controller using thetransmitter 758. In another aspect, the controller 750 may process thesignals received from the detector 730 to an extent and telemeter theprocessed data to a surface controller for producing a spectrum and forproviding an in-situ estimate of a property of the fluid, including thecontamination level of the mud in the formation fluid.

FIG. 8 is a non-limiting schematic diagram showing a portion of asurface-enhanced Raman spectrometer 800 for estimating a property of afluid according to one embodiment of the disclosure. The exemplaryspectrometer 800 shown includes a chamber 816 for holding a fluid 820 tobe analyzed. The fluid 820 may be stationary or it may be passingthrough the chamber 816. The chamber 816 includes a window 814 forallowing light to pass to the fluid 820. The spectrometer 800 includesan electromagnetic energy source 810 that emits electromagnetic energy812 having one or more selected wavelengths. In one or more embodiments,the electromagnetic energy source 810 may be a laser emitting severaldesired wavelengths or bands of wavelengths. A controller 750, similarto the controller 750 described above and shown in FIG. 7, controls theoperation of the electromagnetic energy source 810 to modulate thesource output. The light path from the electromagnetic energy source 810to the window 814 may be an optical fiber such as the fiber 620described above and shown in FIG. 6. The incident energy 812 enters thechamber 816 through the window 814 at a selected angle. The Ramanscattered light 824 from the fluid 820 leaves the window 814. Asemiconductor detector 830, which may be a SiC detector or may be anitride-based detector such a GaN detector described above and shown inFIG. 4, detects the Raman spectra. A processor 752 receives the signalsfrom the detector 830 and processes the signals to estimate a propertyof the fluid 820. The controller 750 may further include memory 754 andprograms 756 for storing information and for controlling the tool.Likewise, a transmitter 758 may be used for communication withsurface-located components.

Fluorescence can interfere with the Raman signals, so to increase theintensity of the Raman signal, an inside surface of the chamber 816including the inside surface of the window 814 may be coated withconductive particles 826. The conductive particles 826 may be placed inthe form of scattered metallic particles, a lattice type structure, orin any other suitable form that will enhance the Raman scattered light.The conductive particles can enhance the Raman Effect due to Plasmonresonance, which consists of energy exchange between the Raman signalsand a surface wave that exists in a conductive layer, such as the layerof particles 826. The spectrometer 800 may be used downhole for in-situanalysis of a fluid, such as the fluid withdrawn from a formation or atthe surface, to estimate one or more properties or characteristics ofthe fluid.

Having described above the several aspects of the disclosure, oneskilled in the art will appreciate several particular embodiments usefulin estimating one or more properties of a downhole fluid in-situ.

In one particular embodiment, an apparatus for estimating a property ofa downhole fluid includes a carrier that is conveyed in a borehole, anda semiconductor electromagnetic energy source carried by the carrier,the semiconductor electromagnetic energy source having an active regionthat includes one or more nitride-based barrier layers that aremodulation-doped using a nitride-based doped layer.

Another particular embodiment for estimating a property of a downholefluid includes a semiconductor electromagnetic energy source thatcomprises a UV electromagnetic energy emitter. In one embodiment, the UVelectromagnetic energy emitter includes a UV laser.

Another particular embodiment for estimating a property of a downholefluid includes one or more nitride-based barrier layers that include atleast one InGaN layer. The nitride-based doped layer may include ap-doped layer, and the p-doped layer may include AlGaN.

Another particular embodiment for estimating a property of a downholefluid includes a nitride-based doped layer comprising a p-blocking layerthat is disposed between two barrier layers.

In yet another particular embodiment for estimating a property of adownhole fluid, a detector responsive to an interaction between theemitted electromagnetic energy and the downhole fluid may be used,wherein the downhole fluid property is estimated at least in part usingan output signal from the detector. In one or more embodiments, thedetector comprises a SiC photodetector or a GaN photodetector. Theoutput signal may be indicative of a downhole fluorescence property.

Another particular embodiment for estimating a property of a downholefluid includes a semiconductor electromagnetic energy source that emitsmonochromatic electromagnetic energy.

Another particular embodiment for estimating a property of a downholefluid includes a semiconductor electromagnetic energy source thatincludes one or more quantum wells, quantum wires, quantum dots andquantum dashes.

A method for estimating a property of a downhole fluid includesconveying a carrier in a borehole and carrying a semiconductorelectromagnetic energy source in a borehole using the carrier, thesemiconductor electromagnetic energy source having an active region thatincludes one or more nitride-based barrier layers that aremodulation-doped using a nitride-based doped layer. The method mayfurther include emitting electromagnetic energy from the emitter towardthe downhole fluid in-situ and detecting an interaction between theemitted electromagnetic energy and the downhole fluid using a detector.The downhole fluid property is estimated at least in part using anoutput signal from the detector.

A particular method for estimating a property of a downhole fluidincludes emitting electromagnetic energy in the form of monochromaticelectromagnetic energy, narrow band electromagnetic energy, wide bandelectromagnetic energy or a combination thereof.

In one particular method for estimating a property of a downhole fluid,emitting electromagnetic energy includes emitting electromagnetic energyof at least one UV wavelength.

One particular method for estimating a property of a downhole fluidincludes detecting an interaction between emitted electromagnetic energyand the downhole fluid using a semiconductor SiC photodetector.

Another particular method for estimating a property of a downhole fluidincludes detecting a fluorescence property of the downhole fluid.

The present disclosure is to be taken as illustrative rather than aslimiting the scope or nature of the claims below. Numerous modificationsand variations will become apparent to those skilled in the art afterstudying the disclosure, including use of equivalent functional and/orstructural substitutes for elements described herein, use of equivalentfunctional couplings for couplings described herein, and/or use ofequivalent functional actions for actions described herein. Suchinsubstantial variations are to be considered within the scope of theclaims below.

Given the above disclosure of general concepts and specific embodiments,the scope of protection is defined by the claims appended hereto. Theissued claims are not to be taken as limiting Applicant's right to claimdisclosed, but not yet literally claimed subject matter by way of one ormore further applications including those filed pursuant to the laws ofthe United States and/or international treaty.

1. An apparatus for estimating a property of a downhole fluidcomprising: a carrier that is conveyed in a borehole; and asemiconductor electromagnetic energy source carried by the carrier, thesemiconductor electromagnetic energy source having an active region thatincludes one or more nitride-based barrier layers that aremodulation-doped using a nitride-based doped layer.
 2. An apparatusaccording to claim 1, wherein the carrier includes a wireline, a drillstring, a slick line, a drilling sub, a BHA, or a combination thereof.3. An apparatus according to claim 1, wherein the semiconductorelectromagnetic energy source comprises a UV electromagnetic energyemitter, a violet electromagnetic energy emitter or a combinationthereof.
 4. An apparatus according to claim 1, wherein theelectromagnetic energy source includes a UV laser, a violet laser or acombination thereof.
 5. An apparatus according to claim 1, wherein theone or more nitride-based barrier layers include at least one InGaNlayer.
 6. An apparatus according to claim 1, wherein the nitride-baseddoped layer comprises a p-doped layer.
 7. An apparatus according toclaim 6, wherein the p-doped layer includes AlGaN.
 8. An apparatusaccording to claim 1, wherein the nitride-based doped layer comprisesp-blocking layer that is disposed between two barrier layers.
 9. Anapparatus according to claim 1 further comprising a detector responsiveto an interaction between the emitted electromagnetic energy and thedownhole fluid, wherein the downhole fluid property is estimated atleast in part using an output signal from the detector.
 10. An apparatusaccording to claim 9, wherein the detector comprises a SiCphotodetector.
 11. An apparatus according to claim 9, wherein the outputsignal is indicative of a downhole fluorescence property.
 12. Anapparatus according to claim 1, wherein the semiconductorelectromagnetic energy source emits monochromatic electromagneticenergy.
 13. An apparatus according to claim 1, wherein the semiconductorelectromagnetic energy source includes one or more quantum wells.
 14. Anapparatus according to claim 1, wherein the semiconductorelectromagnetic energy source includes one or more of quantum wires,quantum dots and quantum dashes.
 15. A method for estimating a propertyof a downhole fluid comprising: conveying a carrier in a borehole;carrying a semiconductor electromagnetic energy source in a boreholeusing the carrier, the semiconductor electromagnetic energy sourcehaving an active region that includes one or more nitride-based barrierlayers that are modulation-doped using a nitride-based doped layer;emitting electromagnetic energy from the emitter toward the downholefluid in-situ; detecting an interaction between the emittedelectromagnetic energy and the downhole fluid using a detector; andestimating the downhole fluid property at least in part using an outputsignal from the detector.
 16. A method according to claim 15, whereinemitting electromagnetic energy includes emitting monochromaticelectromagnetic energy, narrow band electromagnetic energy, wide bandelectromagnetic energy or a combination thereof.
 17. A method accordingto claim 15, wherein emitting electromagnetic energy includes emittingelectromagnetic energy within a UV range, within a violet range orwithin a range including UV and violet wavelengths.
 18. A methodaccording to claim 15, wherein detecting an interaction between theemitted electromagnetic energy and the downhole fluid using a detectorincludes using a detector that includes a semiconductor SiCphotodetector.
 19. A method according to claim 15, wherein detecting aninteraction between the emitted electromagnetic energy and the downholefluid includes detecting a fluorescence property of the downhole fluid.